This invention relates to novel collectors for the recovery of metal-containing sulfide minerals and sulfidized metal-containing oxide minerals from mineral ores by froth flotation.
Flotation is a process of treating a mixture of finely divided mineral solids, e.g., a pulverulent ore, suspended in a liquid whereby a portion of such solids is separated from other finely divided mineral solids, e.g., clays and other like materials present in the ore, by introducing a gas (or providing a gas in situ) in the liquid to produce a frothy mass containing certain of the solids on the top of the liquid, and leaving suspended (unfrothed) other solid components of the ore. Flotation is based on the principle that introducing a gas into a liquid containing solid particles of different materials suspended therein causes adherence of some gas to certain suspended solids and not to others and makes the particles having the gas thus adhered thereto lighter than the liquid. Accordingly, these particles rise to the top of the liquid to form a froth.
Various flotation agents have been admixed with the suspension to improve the frothing process. Such added agents are classed according to the function to be performed: collectors, for sulfide minerals including xanthates, thionocarbamates and the like; frothers which impart the property of forming a stable froth, e.g., natural oils such as pine oil and eucalyptus oil; modifiers such as activators to induce flotation in the presence of a collector, e.g., copper sulfate; depressants, e.g., sodium cyanide, which tend to prevent a collector from functioning as such on a mineral which it is desired to retain in the liquid, and thereby discourage a substance from being carried up and forming a part of the froth; pH regulators to produce optimum metallurgical results, e.g., lime, soda ash and the like.
The phenomena which makes flotation a particularly valuable industrial operation appear to be largely associated with selective affinity of the surface of particulate solids, suspended in a liquid containing entrapped gas, for the liquid on the one hand, the gas on the other.
The specific additives used in the flotation operation are selected according to the nature of the ore, the mineral sought to be recovered, and the other additives which are to be used in combination therewith.
Flotation is employed in a number of mineral separation processes among which is the selective separation of metal-containing sulfide minerals such as those containing copper, zinc, lead, tin, molybdenum and other metals from sulfide minerals containing primarily iron such as pyrite or pyrrhotite.
Once recovered, the metal-containing minerals are converted to the more useful pure metal state, often by a smelting process. Such smelting processes can result in the formation of volatile sulfur compounds. These volatile sulfur compounds are often released to the atmosphere through smokestacks, or are removed from such smokestacks by expensive and elaborate scrubbing equipment.
Among collectors commonly used for the recovery of metal-containing sulfide or sulfidized metal-containing oxide minerals are xanthates, dithiophosphates, and thionocarbamates. Unfortunately, the xanthates, thionocarbamates, and dithiophosphates are not particularly selective in the recovery of sulfide or sulfidized oxide minerals. For example, many nonferrous metal-containing sulfide minerals are found naturally in ore which also contains iron-containing sulfide minerals. When the iron-containing sulfide minerals are recovered in flotation processes along with the nonferrous metal-containing sulfide minerals or sulfidized metal-containing oxide minerals, there is excess sulfur present which is released in the smelting processes resulting in an undesirably high amount of sulfur present during the smelting operations. The xanthates, thionocarbamates and dithiophosphates do not selectively recover nonferrous metal-containing sulfide minerals in the presence of iron-containing sulfide minerals. On the contrary, such collectors collect and recover all metal-containing sulfide minerals.
Other materials commonly recognized as useful in the recovery of sulfide-containing metal or sulfidized metal oxide values include mercaptans. Unfortunately, the mercaptan collectors have an environmentally undesirable odor, are very slow kinetically in the flotation of metal sulfides and do not selectively recover nonferrous metal sulfides in the presence of ferrous sulfides. Therefore, mercaptans are not generally used commercially.
It has also been proposed in U.S. Pat. No. 1,774,183 to use compounds of the formula R--S.sub.x --R' wherein R and R' stand for the same or different alkyl or aralkyl hydrocarbon radicals or groups such as CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, C.sub.4 H.sub.9, C.sub.5 H.sub.11, C.sub.6 H.sub.5 CH.sub.2 or the like and x signifies the number 1 or a number greater than 1. (See, for example, U.S. Pat. No. 1,774,183.) Although the reference teaches that R and R' can be the same or different and that x can be 1, if x is 1, R and R' are the same in the only exemplified compounds. Moreover, of the described compounds, those of the formula R--S--S--R' are particularly preferred. The exemplified materials have not been found to be particularly selective in the recovery of metal-containing sulfide or oxidized metal-containing sulfide minerals, particularly those minerals which do not contain copper.
Similarly, U.S. Pat. No. 4,274,950 teaches using a compound of the formula R--S--R' wherein R and R' are the same or different and are a saturated or unsaturated organic radical. Although R and R' can be unsubstituted hydrocarbon radicals such as alkyl groups, the preferred compounds are substituted with either a hydroxy or carboxy group, e.g., are of the formulas R--S(CH.sub.2).sub.n OH or R--S(CH.sub.2).sub.n --COOR". All the specifically exemplified materials are substituted with a hydroxy or carboxy group except one compound wherein R is a C.sub.12-18 alkyl group and R' is a C.sub.1-6 alkyl group. Again, the exemplified materials have not been found to be particularly selective in the recovery of metal-containing sulfide or sulfidized metal-containing oxide minerals, particularly those minerals which do not contain copper.
In addition, the disulfides and higher sulfides are generally slow kinetically in the recovery of metal-containing sulfide minerals.
In view of the foregoing, a flotation collector which will selectively recover, at good rates and selectivity, metal-containing sulfide and sulfidized metal-containing oxide minerals, including the recovery of nonferrous metal-containing sulfide minerals or sulfidized metal-containing oxide minerals in the presence of sulfide or sulfidized oxide minerals containing primarily iron is desired.